The most common and most likely answer to this crossword clue is the 4 letter word PUNY
I've seen this crossword clue in The Times
P
U
N
Y
More clues leading to the result PUNY
- Small play on words ending in hilarity
- Finished with recession, US city is in need of development
- Weak play on words, ultimately ropey
- Joke ultimately unsavoury and feeble
- Small article from Grasse among peripheral items of perfumery
- Rolled up joint we’re told is undersized
- Feeble joke — start to yawn
- Feeble witticism by Yankee
Buddy explains!

The straight part
We know that "Weak" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case weak = puny.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PUNY mean?
PUNY noun- (Oxford University slang) A new pupil at a school etc.; a junior student.
- A younger person.
- A beginner, a novice.
- An inferior person; a subordinate.
- Of inferior size, strength or significance; small, weak, ineffective.